In standard methods of obtaining metallic lead from concentrates, the standard procedure has been to treat the lead sulfide concentrates in a blast furnace. However, the pyrometallurgical procedure possesses many disadvantages and drawbacks. Primary among these disadvantages is that the process will result in some major pollution problems such as the generation of sulfur oxide gas along with substantial fuming. The fuming carries with it possible carcinogenic compounds which will contain lead, cadmium, etc. Therefore, it is necessary to provide improved and safer methods for obtaining metals such as lead in metallic or elemental form by methods which will not contribute to pollution of the air or will be safer to operate. The aforementioned lead smelting techniques will consist of roast sintering the lead sulfide concentrate whereby a major portion of the sulfur will be removed followed by melting in a blast furnace to obtain the metallic lead.
In an effort to alleviate the pollution problem it is necessary to develop new processes for obtaining lead which will be competitive as an alternative to the conventional smelting practices. Prior work in the hydrometallurgical field resulted in developing a non-aqueous processing route whereby lead sulfide concentrates are chlorinated at temperatures above 300.degree.C. to produce lead chloride and volatilized sulfur. However, chlorination at these elevated temperatures will promote the formation of volatile chlorides of contaminating elements such as iron, magnesium, aluminum, silicon, zinc as well as elemental sulfur which may be present in the lead sulfide concentrate. Other hydrometallurgical processes which have been developed include the use of ferric sulfate as a leach agent. In this method, the lead sulfide is sulfated to form lead sulfate. This step is then followed by carbonation of the lead sulfate to form lead carbonate and thereafter the lead carbonate is subjected to dissolution in hydrofluosilicic acid for electrolysis to metallic lead. Yet another hydrometallurgical method which was developed for the recovery of lead is based on the use of an acidic ferric chloride medium. This method involves a leaching step whereby the lead sulfide is converted to lead chloride and thereafter subjected to steps of solubilizing, crystallization and electrolysis to obtain the pure metal.
As will hereinafter be shown in greater detail, it is now possible to produce metallic lead in a relatively simple and economical manner by fluorinating lead sulfide at a relatively low temperature as contrasted to the prior art methods which have involved chlorination at relatively high temperatures with the attendant formation of undesirable compounds.
This invention relates to a hydrometallurgical process for the recovery of metallic lead. More specifically, the invention is concerned with an improved process for obtaining metallic lead from lead sulfide concentrates whereby unwanted side reactions are minimized and the metallic lead may be recovered in a relatively pure state.
It is therefore an object of this invention to provide an improved process for the production of metallic lead.
A further object of this invention is to provide a hydrometallurgical process for the production of metallic lead from lead sulfide concentrates.
In one aspect an embodiment of this invention resides in a process for the production of metallic lead which comprises the steps of: (1) treating a lead sulfide feed stock with a fluorinating agent, (2) dissolving the resultant lead fluoride in hydrofluosilicic acid, (3) separating the solid residue, (4) subjecting the clarified acid leach solution to electrolysis, and (5) recovering the resultant metallic lead.
A specific embodiment of this invention is found in a process for the production of metallic lead which comprises the steps of fluorinating lead sulfide by treatment with fluorine gas at a temperature in the range of from about 80.degree. to about 120.degree. C., dissolving the resultant lead fluoride in hydrofluosilicic acid at a temperature in the range of from about ambient to about 120.degree. C., separating the solid residue from the acid solution, subjecting the acid solution to electrolysis and recovering the resultant metallic lead.